This invention pertains generally to valves and more particularly to valves having a double seal element so that each seal can be utilized to block the flow of fluid through the valve.
In more particularity, the invention relates to the seal pistons of spherical valves in which the installation handles large volumes of fluid such as is usual in hydraulic turbine installations.
Large spherical valves have a rotor which is rotatably disposed within the valve body for positioning movement between open and closed positions. Normally one seal element is on the rotor and the other cooperating seal element is on the valve body. In spherical valves, a fluid passageway is provided in the rotor with its axis displaced 90 degrees of the axis of the rotor seal element. The rotor is positionable to align the passageway therein with the fluid passageway through the valve body to permit fluid flow through the valve. Positioning movement of the rotor to a closed position displaces the rotor fluid passageway to block the flow of fluid flow through the valve. This movement also aligns the rotor seal element with the valve body seal element to prevent leakage of the fluid around the rotor.
The rotating of the rotor between open and closed positions causes wear to occur on the seal elements. Also, grit matter in the down rushing water flow causes wear on the seal. Whatever the cause of wear, the downstream seal must be periodically serviced. In order to serve the downstream seal elements, it is necessary to provide upstream seal elements which are effected in preventing fluid leakage around the rotor. However, it has been found that the frictional engagement between the rotor sealing elements and valve casing sealing element is not sufficient to prevent fluid leakage around the rotor. Also, due to requirements by OSHA safety factors must be provided to insure positive sealing engagement between sealing elements.
Prior art presently known which attempted to provide some forms of forceful engagement between the sealing elements are exemplified in U.S. Pat. No. 3,532,320 which provides auxiliary sealing elements which interrupt the flow of fluid while the normal sealing elements are being serviced. This patent teaches the utilization of sealing elements on the rotor with one or the other of the valve casing sealing elements. U.S. Pat. No. 3,077,902 teaches the utilization of a spring clip to urge the sealing element into sealing engagement with the rotor. U.S. Pat. No. 3,067,978 teaches the utilization of line pressure from the upstream side to force the upstream seat into engagement with the surface of rotor. The construction of the seal is in the form of a wedge and the pressure forces the seal member towards the apex of the wedge. U.S. Pat. No. 3,013,766 teaches the use of a movable downstream sealing ring adapted to be moved into engagement with a seal ring. The sealing ring is in the form of a piston and fluid pressure utilized to move the sealing ring into or out of engagement with the seal ring. Also shown is an upstream arrangement which is similar to the downstream sealing arrangement. Associated with the upstream sealing arrangement is a fluid actuated sensing device which follows the sealing piston and gives exterior indication of the sealing piston position. Other U.S. patents which teach the utilization of fluid pressure to move a sealing ring into engagement with a rotor seal are U.S. Pat. Nos. 3,007,490; 2,950,896; 2,857,130 and 2,653,004.
However, none of the known prior art teaches of providing a positive mechanical locking means for the sealing piston for positively locking the sealing piston in sealing engagement with the valve rotor. The invention herein disclosed contemplates a novel method for effecting a positive locking of the sealing piston in sealing engagement with the valve rotor and discloses a novel means for practicing the method. In addition, a detecting means is incorporated to sense the position of the sealing piston which is also mechanical in nature.